structure and function of the kidney I Flashcards
kidney location
just below the liver
posteriorly
protected partially by ribs
adrenal gland on top of each kidney, endocrine function
Vascular supply to the kidneys
renal artery/vein
aorta branches into renal artery which delivers blood
renal vein carries blood kidney to vena cava
Hilum
opening for attachment of vasculature (renal artery and vein)
Hilum opens into central cavity known as renal sinus
kidney function
filtration and modification of fluids
regulate water and electrolyte balance
Remove waste products eg urea and eliminate them in the urine
urinary tract
transportation/storage of urine
renal fascia
connective tissue anchor
adipose capsule
support and shock
Between renal capsule and renal fascia (fascia outermost)
renal capsule
connective tissue/ tough fibrous layer surrounding the kidney and covered in a layer of fat known as the adipose capsule of kidney.
path of urine drainage
collecting duct papillary duct in renal pyramid minor calyx (funnel) major calyx renal pelvis ureter urinary bladder
path of blood flow
renal artery segmental arteries interlobar arteries afferent arterioles (very small, in contact with nephron) glomerular capillaries efferent arterioles peritubular capillaries various veins (incl interlobular) renal vein
Bowman’s capsule
site of filtration
has 2 layers- inner (visceral-associated with an organ) epithelium and paretial, outer epithelium
inner is covered with podocytes
Proximal tubule
tubule closest to bowman’s in a network of tubules
cortex
all bowman’s capsules, proximal and distal tubules
outer region of kidney
medulla
loops of henle and collecting ducts
inner region of kidney
juxtamedullary nephron
next to medulla
capillaries here are called vasa recta
make up 15% of nephrons
proximal tubule structure
convoluted
simple cuboidal epithelium with microvilli
brush border provides large SA for processes (reabsorption)
and lots of mitochondria for active processes
descending limb of loop of henle
thin
flattened simple squamous epithelium
ascending limb
thick
simple cuboidal epitheium with no microvilli
cuboidal epithelium
specialised for diffusion
renal corpuscle
site of filtration
bowman’s capsule + glomerulus
3 filtration barriers between glomerulus capillaries and bowman’s capsule lumen
Fenestrated capillaries- large gaps between endothelial cells (but not big enough for cells to pass through, allow all components of blood plasma to pass)
Basal lamina- thin layer of ECM, between endothelial cells and podocytes, acts as a big sieve- prevents filtration of larger proteins
Podocytes are narrow filtration slits- finest level of filtration- prevents filtration of medium sized proteins.
Filtered material moves across these barriers into the lumen of the bowman’s capsule
glomerular filtrate
ultrafiltrate
contains water and dissolved solutes (water and electrolytes, glucose, AAs, waste prducts, urea), only trace amounts of protein (small), ions
filtration fraction
20% amount of substance filtered from plasma into capsule (20% of total renal blood flow)
What drives filtration
hydrostatic pressure of glomerular capillaries (Ph) ie pressure exerted on the wall of the vessel
What is the hydrostatic pressure opposed by
Pfluid: hydrostatic pressure of fluid in the bowman’s capsule
Pi: colloid or oncotic pressure of plasma proteins
How to work out net filtration pressure
Ph - Pi - Pfluid
Glomerular filtration rate
volume of filtrate produced by the kidneys per minute
Despite a net filtration pressure of only 10 mmHg, volume of filtrate is large because:
SA of capillaries large
Glomerular capillary endothelium is fenestrated
Glomerular capillary BP is high
If there is increased resistance in the afferent arteriole
there is incr blood flow to other organs
and decr RBF
Decreased GFR
If there is increased resistance in the efferent arteriole
Decreased RBF, increased Ph and GFR
amount of solute excreted =
amount filtered - amount reabsorbed + amount secreted from blood
What proportion of fluid and solutes are reabsorbed in the proximal convoluted tubule
65%
proximal tubule reabsorption and secretion
lots of reabsorption, some secretion
osmorality same at end of proximal tubule
ureter
transports urine formed in the kidney to the bladder for storage prior to secretion
where are nephrons located
mostly in the cortex, but some extend into the medulla
5 regions of the nephron overview
- renal corpuscle filters blood
- proximal tubule reabsorbs electrolytes, nutrients and water. 2/3 of electrolytes and water filtered from the blood returned
- Loop of Henle creates osmotic gradient by reabsorbing water and electrolytes differentially along its length- gradient allows kidney to concentrate urine.
- Distal tubule reabsorbs electrolytes and water (under hormonal control)
- collecting duct, more water reabsorbed (hormonal control)
filtrate that exits proximal tubule
high in wastes, low in nutrients, greatly reduced in volume
More detail of loop of henle osmotic gradient
Osmolarity of filtrate inside loop low in cortex and high in the medulla
water lost by osmosis as it moves from low solute conc in tubule into higher solute conc in surrounding tissue.
More concentrated as flows deeper into medulla, then solutes move out passively as fluid rounds bend, then in ascending limb ions pumped out so becomes less concentrated
distal tubule cell types
simple cuboidal epithelium with little microvilli
